fn main() {
    // In general, the `{}` will be automatically replaced with
    // any arguments. These will be stringified
    println!("{}", 31);

    // Positional arguments can be used. Specifying an integer inside `{}`
    // determines which additional argument will be replaced. Arguments start
    // at 0 immediately after the format string.
    println!("{0}, this is {1}. {1}, this is {0}", "Alice", "Bob");
    // there will be a complier error, if we use index bigger than length of arguments, just as the following code
    // when compile this code, compiler will report: invalid reference to positional argument 2
    // println!("{0}, this is {1}. {1}, this is {0}{2}", "Alice", "Bob");

    // Placeholder names can be used, but they'll be replaced with the
    // value of their corresponding argument.
    println!("{subject} {verb} {object}",
             subject = "the quick brown fox",
             verb = "jumps over",
             object = "the lazy dog");
    // there will be a complier error, if we use placeholder name not exists, just as the following code
    // the compiler will report: cannot find value `object1` in this scope
    // println!("{subject} {verb} {object1}",
    //          subject = "the quick brown fox",
    //          verb = "jumps over");

    // there will be a compiler error, if we have some arguments not used, just as the following code
    // the compiler will report: named argument never used
    // println!("{subject} {verb} {object}",
    //          subject = "the quick brown fox",
    //          verb = "jumps over",
    //          object = "the lazy dog", 
    //          extra="whatever");

    // Different formatting can be invoked by specifying the format character
    // after a `:`.
    println!("Base 10:               {}",   69420); // 69420
    println!("Base 2 (binary):       {:b}", 69420); // 10000111100101100
    println!("Base 8 (octal):        {:o}", 69420); // 207454
    println!("Base 16 (hexadecimal): {:x}", 69420); // 10f2c

    // You can right-justify text with a specified width. This will
    // output "    1". (Four white spaces and a "1", for a total width of 5.)
    println!("{number:>5}", number=1);

    // You can pad numbers with extra zeroes,
    println!("{number:0>5}", number=1); // 00001
    // and left-adjust by flipping the sign. This will output "10000".
    println!("{number:0<5}", number=1); // 10000

    // You can use named arguments in the format specifier by appending a `$`.
    println!("{number:0>width$}", number=1, width=5);

    // Rust even checks to make sure the correct number of arguments are used.
    println!("My name is {0}, {1} {0}", "Bond", "James");
    // FIXME ^ Add the missing argument: "James"

    // Only types that implement fmt::Display can be formatted with `{}`. User-
    // defined types do not implement fmt::Display by default.

    #[allow(dead_code)] // disable `dead_code` which warn against unused module
    struct Structure(i32);

    // This will not compile because `Structure` does not implement
    // fmt::Display.
    // println!("This struct `{}` won't print...", Structure(3));
    // TODO ^ Try uncommenting this line

    // For Rust 1.58 and above, you can directly capture the argument from a
    // surrounding variable. Just like the above, this will output
    // "    1", 4 white spaces and a "1".
    let number: f64 = 1.0;
    let width: usize = 5;
    println!("{number:>width$}");
}